1. Field of the Invention
The present invention generally relates to RF/microwave antennas. More particularly, the present invention relates to determining radiation patterns of RF/microwave radiators in the presence of numerous conductive surfaces and other simultaneous radiators.
2. Discussion of the Related Art
The ubiquity of wireless communications, as well as other wireless applications such as GPS, etc., has led to the deployment of RF/microwave antennas in a host of environments. For example, RF communications and GPS antennas are commonly installed on vehicles such as cars, boats, and airplanes. In the exemplary case of an automobile with a satellite communications antenna mounted on its roof, the antenna's radiation pattern can be altered significantly by the conducting surfaces of the roof, hood, and trunk of the car. In order to assure an uninterrupted radio link, it is necessary to determine the antenna's far-field radiation pattern in the presence of these sources of interference.
Continuing with the automobile example, the vehicle's metallic surfaces are highly conductive and may be considered as a “ground plane.” As such, radiated energy from the antenna, such as from the antenna's side and rear lobes, induces currents in the metallic surfaces, resulting in a plurality of radiators that interfere with the radiation pattern of the antenna. Accordingly, the entire surface of the automobile may be considered a complex composite radiator.
To determine properly the far-field radiation pattern, it is generally required to determine the far-field radiation pattern of the automobile/antenna combination as well as the far-field pattern of the antenna independent of the effects of the automobile's metallic surfaces.
It is impractical to measure the far-field radiation pattern for an object the size of an automobile. Accordingly, near-field scanning is typically done, followed by transformation techniques that convert the measured near-field pattern to a far-field pattern. However, there are problems in related art approaches to performing the near-field scan. It is extremely difficult to measure the near-field radiation pattern of the car with the antenna, and to filter out the effects of the car on the antenna's far-field radiation pattern computed from the near-field scan. First, related art approaches to filtering the effects of the car from data derived from the near-field scan require that the antenna be located at the origin of the scan coordinate axes. Further, near-field scanning requires that the antenna's radiation pattern be measured in a spherical scan pattern that encompasses the entire automobile. Accordingly, related art filtering techniques require an elaborate gantry and turntable whereby the rotation axis of the gantry and the rotation axis of the turntable intersect at the antenna. Given the location of the antenna on the automobile, this is generally impracticable. Second, it is extremely difficult to determine the far-field radiation of the pattern without secondary radiative effects of the automobile itself.
Although the above discussion uses an automobile as an example, the same issues arise with other vehicles, such as airplanes and boats, as well as other types of antenna applications, such as satellite-mounted antennas, phased-array antennas, etc. In any of these cases, the antenna is part of a composite radiator (including the auto body, airplane skin, phased array structure, etc.), the combination of which alters the radiation pattern of the antenna.
Accordingly, what is needed is a system and method for determining the radiation pattern of an antenna as a part of a composite radiator that enables a determination of the far-field radiation pattern of the antenna, while not requiring that the antenna be located at the origin of the coordinate system of the scan mechanism.